The present invention relates to a method for controlling the automatic transmission in a motor vehicle having an engine, wheels, a wheel slip control system and an automatic transmission having a clutch.
In a vehicle having automatic transmission, certain roadway conditions can lead to less than optimal performance of the automatic transmission during gear shifting. For one example, icy, wet, or otherwise slippery road surfaces may result in wheel slippage immediately following a gear change. When shifting up on a slippery surface, there is a danger of wheel slippage in the positive direction (drive slip). Also, when downshifting on a slippery road surface, there is a danger of wheel slippage in the negative direction (brake slip).
Another example of less than optimal performance of the automatic transmission during gear shifting occurs when starting the vehicle from rest in conditions where there is a high resistance to travel, e.g. a steep roadway inclination, deep snow, etc. When the vehicle begins to move from rest, the automatic transmission is in the start mode, and thus it allows the clutch to slip until a certain minimum vehicle speed is obtained. In situations where there is a high resistance to vehicle travel, such as when the vehicle is on an upward incline or in deep snow, the vehicle usually takes longer to reach the minimum vehicle speed leading to a heat load and faster wear of the clutch. In some circumstances it can lead to permanent damage to the clutch.
in vehicles having a wheel slip control system, understood here to be a system capable of determining the friction coefficients between the wheel and the roadway surface, the slippage of the wheel, the wheel speed and the vehicle speed. Signals that are generated based upon these values can be used to improve transmission control to help eliminate the aforementioned problems. Examples of wheel slip control systems include antilock braking systems (xe2x80x9cABSxe2x80x9d), traction control systems (xe2x80x9cTCSxe2x80x9d or xe2x80x9cASRxe2x80x9d), automatic brake force differential lock systems (xe2x80x9cABS/ADSxe2x80x9d), or electronic stability program (xe2x80x9cFDR or ESPxe2x80x9d).
The present invention relates to a method of controlling a drive train of a motor vehicle having an engine, a wheel slip control system, and an automatic transmission having a clutch, characterized in that the automatic transmission is controlled based upon signals generated by the wheel slip control system.
In an exemplary embodiment of the present invention, the automatic transmission can be controlled to reduce wheel slippage on slippery road surfaces based upon signals indicating that a coefficient of friction between a wheel and a roadway surface are less than a predetermined friction coefficient value. A signal indicating the current engine speed may also be used. The automatic transmission can be controlled by controlling the closing of the clutch including controlling both when, and how quickly, the clutch is closed. For example, the clutch can be closed more slowly if the engine speed is not at or near a target engine speed for the gear being shifted into. The closer the engine speed is to the target engine speed, the more quickly the clutch can be closed without danger of wheel slippage. In another exemplary embodiment, the automatic transmission is controlled by adjusting the engine speed in addition to controlling the closing of the clutch. The engine speed can be adjusted, for example by controlling the throttle valve angle, to more closely approximate a target engine speed value.
In another exemplary embodiment, when trying to start a vehicle from rest in high resistance conditions, the automatic transmission is controlled when the vehicle speed is less than a predetermined vehicle speed and an elapsed time since vehicle start is greater than a predetermined time value. In place of comparing time, the number of slip cycles of the clutch may be compared with a corresponding predetermined value. When the wheel slip control system indicates that the vehicle speed is less than a predetermined vehicle speed value and the time since vehicle start is less than a predetermined time, the automatic control system can be controlled by increasing the engine speed and closing the clutch, thus alleviating unneeded strain on the clutch.